262 PRIMAR}- ARRANGEMENT OF TISSUES. 



a. Simf-le type of the Palms. 



Since Mohl's Anatomy of Palms ^ the following chief characteristics have been 

 known for this type. 



All bundles of the cylinder (with doubtful, and extremely unimportant exceptions 

 to be mentioned below) are bundles of the leaf-trace. The base of the leaf encloses 

 the whole circumference of the stem, or at least the greater part of it. The leaf- 

 trace always consists of a number of bundles, and usually of many, in strong shoots 

 of tw^o hundred bundles : its width is \ of the circumference of the stem, or more, or 

 not much less. The bundles curve from the base of the leaf into the cylinder, and 

 pass downwards in the latter ; some at its surface, running almost radially perpendi- 

 cular; others are radial and oblique, penetrating first in a curve convex upwards 

 and inwards, towards the longitudinal axis of the cylinder, then turning outwards 

 and gradually passing towards the surface of the cylinder; as they approach it, they 

 assume an almost perpendicular position. All bundles desceiid through many 

 internodes, and finally unite in the outer portions of the cylinder with such as 

 emerge lower down, inserting themselves on these sometimes in a tangential, 

 sometimes in a radial or oblique direction. Up to this point of insertion at their 

 lower ends the bundles pursue an individual course. The coalescence of the lower 

 ends of descending bundles with such as emerge lower down occurs with such 

 frequency that the whole number of the bundles in equally strong successive inter- 

 nodes remains about the same. Where the successive internodes and leaves grow 

 stronger the number of the bundles increases, and vice versa. The number of the 

 internodes which a bundle traverses cannot be exactly defined. 



Further, the bundles of a leaf-trace, which curve towards the middle of the 

 cylinder, do not all penetrate to the same depth ; on an average the median bundle 

 of a series penetrates the deepest, the others less deeply the further they are from 

 the median one, the marginal ones pass almost perpendicularly down the surface 

 of the cylinder: w'here there are several series, those of the inmost penetrate 

 as a rule deeper than those of the outer, which are equally distant from the 

 median bundle. 



The necessary consequences of the course described are, firstly, that the bundles 

 in the transverse section of an iniernode are more crowded the nearer they are to 

 the surface of the cylinder, a phenomenon which is especially striking where the 

 bundles are distributed over the whole surface of section of the cylinder. Secondly, 

 that the successive traces pectinate, and cross one another with their curved bundles. 

 Mohl's celebrated scheme, which is here reproduced in Fig. 117, shows this condi- 

 tion in radial longitudinal section, but starting from the incorrect assumption that all 

 bundles of one trace are almost equally curved and are tangential and perpendicular, 

 that is that they lie at the surface of a cone which has a funnel-shaped opening at 

 the top. If it is assumed that the leaves alternate with a divergence of \ and 

 embrace the stem, and that the bundles are tangentially perpendicular, their course 

 in the stem would be represented with greater exactitude by the scheme of a radial 



' De Palmarum Struclura ; Monajhii, 1831 ; Verm. Schr. p. 129; translated in the Ray 

 Society's Reports and Papers on Botany, 1S49. — Niigeli, Beitr. 1. I.e. 



